There is a growing need to reduce the power consumption of static devices and especially of mobile devices. Mobile devices can include, for example, personal data appliances, cellular phones, radios, pagers, lap top computers, and the like. The power consumption of mobile devices is critical as they are usually supposed to operate for relatively long periods before being recharged.
Typical devices have multiple circuits such as processors, controllers, memory units, peripherals and the like. Typically, many circuits are interconnected to each other by a central bus.
When multiple circuits are connected to the same bus each circuit can access the bus, according to a media access control scheme. A device that is allowed to access the bus can write a certain circuit writing value that propagates over the bus.
There is a need to assure that the circuit writing value properly propagates along the bus and is not affected by the output of other circuits. In order to satisfy this need various techniques were developed. These techniques include a “return to zero” and a “return to one” policies that force a circuit to provide a zero or one value when it ends its writing session.
It is known that frequent changes of bus states is energy consuming. Each change in the bus state requires the writing circuit to charge (or discharge) various bus capacitances. Both the return to zero and return to one policies involve multiple bus changes.
High impedance architectures allow circuits to enter a high impedance state and not to affect the bus state during idle periods. High impedance devices have various drawbacks such as larger silicon footprint, testing problems, introduce difficulties in insertion of repeaters, and the like. Some of the drawbacks are illustrated in U.S. patent application 2002/0166074 of Cheung et al.
There is a need to provide an efficient manner to decrease the energy consumption of integrated circuits.